It's a variable thats multiply your prize :P. If you request a payout for a specified address on consecutive days, it'll rise by 0.05 each day (starting from 1). If you miss one day, it'll get back to 1. It can rise up to 2. So, for example, if you get your prize for address XYZ on 10 consecutive days, your multiplier will be equal to 1+9*0.05 = 1.45. So if you get a prize of 0.00005 BTC, you'll actually get 0.00005*1.45 = 0.0000725 BTC! You can check your current multiplier on this page
NOTE: the multiplier works for DAILY prizes, not on the final payout transaction. So your "accumulated" coins already include multiplier bonus.
